The present invention relates to optical integrated circuits in which both a light function zone and a light reception zone (for changing a propagation state of light) are monolithically formed on the same substrate, and which, in order to enhance a light receiving sensitivity, have their improved electrode structures formed on a light wave guide layer and have an improved photoconductive effect of a light reception zone.
It has previously been proposed to form the light function zone which makes use of a piezo-electric effect and the light reception zone for light from this light function zone on separate substrates, as shown in FIG. 1. Take, for example, a spectrum analyzer for electric signal which makes use of light, a light wave guide layer 2 is formed on a substrate 1. An acoustic optical element as a light function element 3 which makes use of a piezo-electric effect is provided on the light wave guide layer 2 on the substrate 1 and in the travel path of light. A transducer 3b connected to a power source 3a generates distortion in the light wave guide layer 2 due to a piezo-electric effect. This distortion propagates through the wave guide layer 2 as an ultrasonic wave causing a change in refractive index of the layer 2. An incident light I.sub.in passes through this zone to produce a diffraction light I.sub.d due to the effects of this acoustic optical element. The diffracted light I.sub.d is received by an image sensor 4 on another substrate (not shown) separate from substrate 1. A disadvantage attendant such an arrangement is that it is difficult to accurately adjust the respective optical axes of the light wave guide layer 2 and the image sensor 4 since they are separately formed, and that difficulty is involved in assembling and reliability is low. Depending upon how light is emitted from the light wave guide layer 2, a scattering and a coupling loss may be caused, thereby incurring a loss of emission and an increase of noise. With the image sensor 4 in which the array is so included in the light reception cell as to be linear and perpendicular to the optical axis, a greater diffraction angle .theta..sub.B +.DELTA.B is obtained, the greater the distance of propagation the more the sensor is subjected to diffusion of beam to permit occurrence of noise thereby lowering the S/N ratio.